Weld Wheels Backspace question

[70cuda69dart]

Hey guys I’m looking to order some Prostars for my 69 dart (stock front end) I know I want 15x4s, just not sure on the backspace. The two choices are 2.50 or 1.875. Any pics or advice to help me out would be appreciated. Planning on running a 26 inch tall tire

 

[pntastar69]

4 piston Calipers or drums?

 

[70cuda69dart]

4 piston Calipers or drums?

discs in the front, I believe they are the later years, stock style discs

 

[Daves69]

Lol, and I thought 5" were skinny.
Barracuda pictures if it helps. These are 15 X 5 - 3-1/2 BS 26" tire '74 Dart manual disc..….

 

[dano]

The 2.5" BS would be flush on the outside of the rim with what Daves69 shows.